Machine for performing operations consecutively at preselected working positions

ABSTRACT

A machine for performing operations consecutively at preselected working positions, such as semi-automatic wiring of electronic circuits, the positions being defined in relation to co-ordinate axes, the machine having on said axes scales consisting of transverse conductive strips, tool carrier slides adapted to short-circuit adjacent strips, and an electronic logic system which compares the short-circuit position with an input representing preselected working positions and signals a drive system to stop the carrier on reaching the selected working position, and reverse to correct overshoot so that the tool carrier is accurately positioned.

United States Patent Bodin [54] MACHINE FOR PERFORMING OPERATIONS CONSECUTIVELY AT PRESELECTED WORKING POSITIONS lnventor: Jacques Bodin, Nantes, France Societe dEtudes, Recherches et Constructions Electroniques S.E.R.C.E.L., Rue de Bel Air, 44 Carquefou, France Feb. 18, 1971 Assignee:

Filed:

Appl. No.:

Foreign Application Priority Data Feb. 18, 1970 France..,. .....7005741 May 26, 1970 France ..7019112 U.S. Cl ..318/602 Int. Cl. ..G05b 19/28 Field of Search ..318/574, 594, 601, 602, 660,

[451 Apr. 25, 1972 [56] References Cited UNITED STATES PATENTS 2,930,030 3/1960 l-lirose ..318/602 3,020,460 2/1962 Morin ..318/594 3,199,006 8/1965 Moreines.... 18/602 3,356,932 12/1967 Farrand ..318/660 Primary Exan'tiner-Bemard A. Gilheany Assistant Examiner-Thomas Langer Attorney-Oberlin, Maky, Donnelly & Renner [5 7] ABSTRACT 14 Claims, 9 Drawing Figures Patented April 25, 1972 F/Gd 7 Sheets-Sheet 4 Patented April 25, 1972 7 Sheets-Sheet 5 IIIIIIVVVIVII.

9 7674 /2H0987654I/2 0 li llr l l l FIG-6 Patented April 25, 1972 '7 Sheets-Sheet 6 EES??? 3% E: SE E s Si QR R E N wk a my my ox MACHINE FOR PERFORMING OPERATIONS CONSECUTIVELY AT PRESELECTED WORKING POSITIONS This invention relates to a machine for performing operations consecutively at a number of positions defined in a direction or working plane by at least one sequence of discrete co-ordinate values. More particularly, the invention relates to a machine of the kind specified in which an indexing or working element is given a controlled positioning at any of a number of places which are the intersections of a notional lattice'or grid having a first pitch (i.e. a series of finite intervals) along an X axis and a second pitch, which may or may not be the same as the first pitch, along a Y axis. Machines of this kind are used to perform repetition operations, such as welding or wire-winding or piercing at the places thus determined.

Some known machines of this kind have two slides or the like providing guidance along two axes, the position of one slide providing an X co-ordinate and the position of the other slide providing a Y co-ordinate; slide movement is controlled by step-by-step motors receiving from an intermediate store, pulses the number of which is characteristic of the required place determined by the two coordinates. These known systems are unsatisfactory. First, there is only an indirect correlation between the pulses and the motor-produced movements, and the various positions of the working surface; the encoding of the positioning is indirect. Since encoding based on the counting of pulses is subject to error, there may be pitch shifts which, if the pitch is small, cannot be detected rapidly.

Also, it may be required to alter the pitch for some purposes, such as for electronic circuit wiring for which at least two standard pitches are used; in this event very-small-step motors must be used to ensure satisfactory definition and to enable the electronic control system to be adapted to the pitch changes. Since there is a limit to the number of steps which can be counted in a second, the movement provided by motors of this kind is slow.

In another known kind of system, an obsolute encoding is used and indications are given representing the position of a movable element on its path. As a rule, systems of this kind display a numerical indication which remains constant while the position of the movable element remains in a given geometric interval, e.g. a measuring unit expressed in millimeters. Systems of this kind cannot be used for consecutive positioning control at accurately defined places by at least one sequence of discrete co-ordinate values.

It is a first object of this invention to provide a machine which can perform consecutive operations and which can operate with absolute encoding of working-station position.

It is another object of the invention to provide a machine of the kind specified which can provide rapid and very accurate positioning.

It is another object of the invention to provide a machine of the kind specified in which pitch-changing can be effected in a simple manner.

It is another object of the invention to provide an electronic circuit wiring machine with fully automatic positioning and semi-automatic performance of the actual wiring operation.

According to the invention, a machine for performing operations consecutively at predetermined working stations comprises: a tool holder or work carrier moved by at least one moving system movable in both senses (i.e. forwards and backwards) along a co-ordinate axis by a drive system; the (or each) moving system being associated with an insulated scale extending along the corresponding co-ordinate axis; each scale having a number of transverse conductive strips insulated from adjacent strips; the (or each) moving system having a member adapted to short-circuit any two adjacent strips of its associated scale in the direction of movement of the moving system;'and an electronic logic circuit adapted to detect a short-circuit between two adjacent strips in registration with a given working station and to initiate stopping of the drive system at the commencement of the short-circuit and to start the drive system, but in the opposite sense, after a predetermined time interval, to provide accurate iterative positioning of the moving system in registration with the working station.

Some embodiments of the invention will now be described by way of example with reference to the accompanying drawings, wherein:

FIG. 1 is a diagrammatic perspective view of an X-Y positioning device embodying the invention;

FIG. 2 is a simplified diagram of the positioning device shown in FIG. 1;

FIG. 3 is a logic diagram of the electronic control system;

FIG. 4 is a diagram to illustrate how a roller can short-circuit to consecutive strips;

FIG. 5 is a plan view of one form of scale;

FIG. 6 is a logic diagram showing the encodings provided by the scale shown in FIG. 4;

FIG. 7 is a plan view of another form of scale and the relevant logic encoding diagram; and

FIGS. 8a and 8b are diagrammatic representations of parts of a logic circuit of the embodiment shown in FIGS. 3 and 4.

Referring to FIG. 1, there is shown an example of the invention as applied to an electronic circuit wiring machine. There can be seen the frame 1 of the machine and the working surface 2 on which the wiring is carried out. The function of the positioning device of the machine is automatically to position a tool positioner member 3, which has a recess 4 to accommodate the wiring tool 5 (see FIG. 2) at a position determined by predetermined values on the X and Y co-ordinates. The member 3 is slidable on a rod 6 which extends parallel to the X axis and which can move in a direction parallel to the Y axis. The member 3 is rigidly secured to a rod 7 which extends parallel to the Y axis and which determines the position of the member 3 on the rod 6, i.e., the X co-ordinate of the place. The rod 6 is secured at each end to a Y guide slide 8, 9, each such slide being slidable on a guide rod l0, 11 respectively disposed on either side of the working surface or area 2 and parallel to the Y axis. The slide 9 has a member 12 through which a tapped bore extends; the bore co-operates with a leadscrew 13 which extends parallel to the guide bar 11 and is rotated by a Y-axis electric motor 14. The rod 7 is slidable in an X-guide slide 16 which is itself slidable on a guide rod 17 parallel to the X axis; the slide 16 is adapted to be moved by an X-axis electric motor 18 by way of a lead-screw 19. This mechanical arrangement enables the member 3 to be placed in any desired position above the working surface 2.

Disposed parallel to the direction of movement of the guide slide 9 is an indexing scale 20 comprising an insulating support 21 on which adjacent conductive strips are separated from one another by gaps 22. Scales of this kind will be described in greater detail hereinafter with reference to FIGS. 4 to 7. The slide 9 has a conductive roller or some other element 24 which can produce a short-circuit across any gap 22.

As will become apparent hereinafter, a command for the member 3 to take up a selected Y co-ordinate position is a matter of testing for the presence or absence of a short-circuit between the two adjacent strips corresponding to the selected Y co-ordinate. The motor 14 moves the slide 9 towards the selected position, as will be seen hereinafter. When the shortcircuit between the two strips associated with the selected position occurs, the motor 14 is stopped so that the member 3 is disposed exactly at the chosen place.

There is a similar scale 25 placed parallel to the path of movement of the slide 16, this scale comprising an insulating support 26 on which is disposed a series of conductive strips separated by gaps 27. A roller or other conducting element 29 can short-circuit any two adjacent strips.

As will be apparent, the length of the movement steps of the member 3 depends upon the distance between two consecutive gaps. To change the length of this step, a scale of one pitch can be replaced by another scale whose gaps are at the appropriate pitch.

If the required number of pitches is small, it is preferable to use a single scale having a number of rows of strips, each row of a different pitch. As will be described hereinafter, the strips may be interconnected in the same order in the various rows so that encoding is the same for all pitches apart from the change of scale. One roller or other short-circuiting member per row of strips must be provided in such multi-pitch systems. If only two pitches are required, a variant is to use a single roller and to turn round the other way a scale having two rows of strips disposed symmetrically with respect to a given center; the symmetry does not extend to the actual strips, which have a different pitch, nor to their interconnections.

FIG. 2 is a diagrammatic view of the'control system for positioning the member 3. The wiring position co-ordinates are recorded on a punched tape 30; in the case under consideration the tape 30 also stores the length of the wires to be used for wiring and the code number of the operation corresponding to each wiring position. The operator depresses a pedal 31 to start a tape reader 32. The data from the tape pass to a logic command and checking unit 33 which initiates operations. The system 33 has under its control a display unit 34 for displaying the operations number, the parity error and coincidence, a slide movementcontrol unit 35, a wiring position detector unit 36, a wire length selector unit 37 and a wiring tool 5. As soon as the tape data have been transmitted to the unit 33, the latter stops reading the tape and displays the operation number 4,937 in the presentcase at the unit 34, displays the wire length at the unit 37, supplies the unit 36 with the X and Y co-ordinates of the new wiring position, and signals to the unit 35 the sense in which the motors 14, 18 must rotate having regard to the previous position of the member 3. A box 38 contains pigeon holes holding wires of various lengths, a tell-tale 39 indicating the pigeon hole containing the wire of the required length.

The detector unit 36 makes connections appropriate for detecting a short-circuit between the appropriate two adjacent Y-co-ordinate strips on the scale and the two consecutive X-co-ordinate strips on the scale 25. When the respective rollers 24, 29 make these short-circuits, the detector unit 36 acts via the control unit 35 to stop the motors 14, 18. The shortcircuit made between two strips by the roller is detected by means of a voltage, a short-circuit signal of complex shape having numerous peaks being produced. This signal is shaped by a monostable circuit triggered by the start of the short-circuit signal. The monostable circuit delivers a square-wave signal of predetermined duration which is used by the logic circuits. In whichever direction the motor runs, the rising or leading edge of the square-wave signal (start of the short-circuit signal) corresponds to a command to stop the motor, the trailing edge of the square-wave signal corresponding to a command to start the motor in the opposite direction.

The reversal of the motor causes a new movement over the scale, a new short-circuit, a new square-wave signal and a new reversal of the running direction of the motor, the process being repeated, for instance, three or four times, in dependence on the initial direction of arrival. After a predetermined number of iterations, which varies by one unit, in dependence on the initial direction of arrival, the slides are braked to lock them in the stopped position. Since the oscillations about the required working position alternate each time, they form a converging series; the point of first arrival is generally not the required working position, but the correct required positions can be attained repeatedly since the last of the iterative movements is always in the same direction.

This form of stopping is independent of the choice of electronic elements (kind of motor), direction of travel, speed of travel, distance travelled, mechanical inertia and friction (indeed, friction increases the convergence of the series of oscillations). Preferably, for more accurate stopping with allowance for various forms of back-lash, inter alia of the roller, as will be seen hereinafter, and for friction, final stoppage and braking of the slides always occur in the same direction under the control of the units 35 and 36.

When the member 3 has stopped, the command unit 33 checks whether it has been stopped after three or after four iterations about the required position the check is affirmative,

or if the new wiring operation is to be performed without the slides having to be moved, the coincidence is displayed by the display unit 34, and the command unit 33 permits the tool 5 to operate. When, and only when, the tool has operated, the command unit 33 restarts the tape reader 32.

FIG. 3 shows in greater detail the logic scheme of the automatic control system for the positioner 3. The reader 32 supplies data read from the tape to a decoder 40 which controls a circuit 41 for cancelling counting operations in a counting unit 42 addressing operations in an addressing unit 43 in response to a cancellation signal. A decoding unit 44 is disposed between the counting unit 42 and the addressing unit 43. The decoder 40 also acts on a stop circuit 45 which signals a stop order to a reader control unit 46, which aiso controls a counting and addressing control unit 47. In the event of a parity error the decoder acts on parity error unit 48 to stop the reader and display the parity error at the display unit 34, and locks all the functions of the machine.

A memory unit 49 receives the X and Y co-ordinates data from the reader 32 and acts via a decoding unit 50 to make the connections appropriate to detect short-circuits on the two scales. A comparator 51 compares the new co-ordinates with the co-ordinates for the previous wiring position so as to signal to the slide movement control unit 35 the directions in which the guide slides must be moved. When the actual position of the tool positioner member 3 coincides with its required position, a wiring permission unit 52 permits wiring tool 5 to operate. Upon the completion of wiring the tool 5 permits a reader restart unit 53 to transmit a restart command to the reader control unit 46. The wiring operation is therefore semiautomatic; the operator positions the wire and controls the wiring, but the selection of the working position is automatic.

Various forms of scale and the associated encoding sub-circuits will now be described with reference to FIGS. 5 to 8b.

A description has already been given with reference to FIG. 1 of a scale 20 comprising an insulated support 21 extending parallel to the direction of movement of the guide slide 9. The scale has n gaps 22between adjacent conductive strips. There are therefore n 1 such strips which are numbered from 0 to n along the co-ordinate axis. The member 24 secured to the guide slide 9 whose positioning it is required to control, shortcircuits two adjacent strips when the guide slide 9 is in an appropriate position. There are therefore n possible positions for n 1 conductive strips. As already stated, the various strips of each scale are connected to an electronic logic circuit adapted to transmit a signal when two adjacent strips are short-circuited and to define which strips must be short-circuited for the slide to be in its required position on its co-ordinate axis. As will be seen hereinafter, the various strips are interconnected to form a sub-circuit which helps to simplify the logic required to process the short-circuit signal and to reduce the number of electrical connections between the conductive strips and the logic circuit. Extra conductive strips may be provided at the ends of each scale to control at least the braking of the associated slide, to prevent it leaving the working zone of the scale.

FIG. 4 shows a preferred embodiment of the short-circuiting element. The conductive strips of the scale 61 project above the insulating support, and the short-circuiting member is a roller 62 mounted on the movable guide slide. The roller 62 runs on the scale 61 and at least the running surface of roller 62 is conductive. The radius of the roller 62 depends upon the size of the gaps between adjacent strips. This radius is so chosen that, even after wear of the strip edges, the roller bears only on the strips and not on the insulating support. Also, since the roller moves in both directions, strip edge wear is virtually symmetrical so that the roller axis is always positioned in relation to the center of any gap, and so positioning stays reliable and accurate,

Advantageously, the roller spindle has a clearance, so that when the slide, and therefore the roller, move fast, the roller can then have a slight dwell in the gap so that the strips are short-circuited for a slightly longer time. The square-wave signal delivered by the monostable circuit to the logic circuits, such as 36, then has a leading edge which is defined more precisely from the short-circuit signal. Control of the stoppage of movement, movement in the opposite direction and braking after the iterations are performed from such square-wave signal, as previously stated.

A description will now be given of various forms of scale and the strips thereon. Advantageously, the scale is a printedcircuit device.

In a first embodiment of the scale as shown in FIG. 5, the strips are all of the same size and are arranged to form two interdigitated combs, and there are also strips which do not form part of either comb. The arrangement is such that any one tooth of either comb is disposed between two strips not forming part of the same comb. The n l conductive strips representing n working positions, are numbered from 0 to n. The odd-number strips are connected individually and separately to the logic circuit by appropriate connections. Alternate even-number strips of the number 2p, p being an even number, namely 0, 4, 8, 12 etc., are connected to a first longitudinal busbar 63 to form a first comb. The other evennumber strips of the number 2 (p 1), namely 2, 6, etc., are connected to a second busbar 65 to form a second comb. Therefore, the number of connections between the scale and the logic circuit is equal to n/2 the integral part of the number (11/2) 2 0.5. Hereinafter the sign llint()ll will be used to denote the function integral part of. These connections are made to wiring position detector unit 36 which, in dependence upon the required position, determines between which odd-number strip and which comb a short-circuit will indicate that the required position has been reached.

In a second embodiment of the scale, there is a considerable reduction in the number of connections between the scale and the unit 36. The minimum number 0 of connections is associated with the number n of strips used by the formula:

This formula represents the number of combinations of the c connections taken in pairs. The strip interconnections required to form the sub-circuit can be obtained by means of a scale having two insulated supports; parallel conductors corresponding to the strips are disposed on one support, and another set of parallel conductors are disposed on the other support perpendicularly to the parallel conductors of the first support, and are connected to connecting bars for the various external connections. The necessary connections between conductors on the first support and conductors on the second are made in the same way as is done for a programming matrix. Preferably, the two supports are the two surfaces of a printed circuit, the interconnections being made through the printed-circuit board. A description of such an arrangement now be given by way of example with reference to FIG. 6, which shows 22 stn'ps giving an indication of 21 positions(i.e. n 1 strips), and seven external connecting bars (i.e. c external connections), the connecting bars being indicated in Roman numerals. The internal connections are represented by small circles at the intersection between horizontal conductors connected to the strips and vertical conductors connected to the bars. First, the seven bars are connected to the first seven strips (connections 0-I, 1-II 6-VII), whereafter the next seven strips are connected to the seven bars alternately (the connections are therefore 7-l, 8-III, 9V 13-VI). Next, every third connecting bar is taken, the last strip being connected to the bar I. All the combinations of strips and connections have then been obtained without repetition and without omission.

In general, if there are 0 connection bars there are:

strips. If r: is a prime number the connection bars are connected to the first c strips (marked from 0 to (c 1)). The next 0 strips are connected to the bars, but missing out every alternate one, whereafter the next 0 strips are connected to the bars, on a one-out-of-three basis, and so on as far as the series of connections made by taking one bar out of (c 1/2), and to finish with, the final strip numbered:

the numbers of the connections corresponding to any given position can be found from the formulae:

a and b being defined by the following formulae:

(3) g=int 1 P Any strip of a scale when associated with an adjacent strip represents a position data bit. The exact position is therefore given by a between-strips gap, as stated in the detailed desc ription with reference to FIG. 1.

In a variant, the sub-circuit connections between the scale strips are on the basis of some conventional form of encoding such as decimal-coded binary encoding l, 2, 4, 8, This slightly increases the number of connections to be made to the wiring position detector unit 36 but considerably simplifies the detection of short-circuiting between the consecutive strips corresponding to a predetermined position, as will be seen hereinafter. One such sub-circuit is shown in FIG. 7, where there can be seen the strips numbered from 0 to n. Except for the end strips, as 70, the even-number strips 2, 4, 6, 8 etc. are constituted by two half-strips insulated from one another, as 72 and 72', 74 and 74' .78 and 78', 710 and 710' etc. The odd-number strips are interconnected in groups of five. The first five odd strips 1 to 9 form a first group called decade 0," strips 1 l to 19 form a second group called decade 1, and so on. As in the embodiment hereinbefore described with reference to FIG. 6, the insulated scale support member can be constituted by two insulated supports, the first of which has the insulated strips and their grouped connections. A second insulated support comprises ten output connections which are shown as horizontal lines in FIG. 7 and which correspond to unit digits, namely 0, l 9. As in the case of the circuit of FIG. 6, interconnections are made between the strips and the aforementioned external connections, the two insulated supports comprising crossed conductors, connected respectively to even half-strips and to external connectors.

interconnections are made as follows:

The 10 units connections are connected to the first ten halfstrips (connections 0-70, l-72, 2-72, 3-74, 4-74 8-78, 9-710), whereafter the units connections are connected to the next ten half-strips, and so on.

A variant, which is very suitable for use in wiring machines, is to use two scales having different pitches, e.g. 2.54 and 3 .96 mm, arranged on the same single-surface printed circuit with decade and units interconnections of the kind described. The

thickness of the copper layer of the strips of each scale is chosen in accordance with the roller diameter and, except for the pitch of the between-strips gaps, the arrangement of this printed circuit is symmetrical about its center. The external connections of the printed circuit are brought to two connectors of known type which are arranged geometrically and electrically in accordance with the symmetry just mentioned. To change the pitch, the printed circuit is turned the other way round in the manner mentioned previously.

As will be apparent, the position of the short-circuiting member is detected by a unit connection being short-circuited to a decade connection. This embodiment can be used to detect more than 99 positions by using 10," l 1 and so on decades. For instance, 200 positions can be detected with twenty decade connections labelled to 19 and units connections, i.e., thirty connections in all.

To obtain a positioning signal, a signal is transmitted via a wiring position detector unit 36 to the corresponding decade and the pulse produced as a result of short-circuiting is detected on the unit connection; for instance, for position 191 a signal is sent to the 19 decade connection and the signal detected on the 1 unit connection is selected.

FIGS. 8a'and 8b are diagrammatic views of a logic control circuit for obtaining the positioning signal for the scale of FIG. 7. The circuit comprises three binary-to-decimal digital converters 81-83 corresponding to the hundreds, tens and units, respectively. The decimal outputs of the hundreds and tens converters are combined to give outputs corresponding to the decades of FIG. 7, the combination being achieved by means of AND-gates, e.g. 84-86, each having two inputs, one connected to one output of the converter 81 and the other to one output of the converter 82. The AND-gate 86 as shown corresponds to the 19 decade. The outputs of the various AND- gates are taken one each to the corresponding decade connection of the insulated scale of FIG. 7. The units connections of such scale go one each to the input of an AND-gate, e.g. 87- 89, whose second input is connected to the corresponding output of the converter 83. The outputs of the AND-gates 87-89 go one each to an OR-gate 90.

The circuit just described operates as follows:

When a workingposition has been selected, the corresponding decimal outputs of the converters 81-83 are energized. The appropriate AND-gate 84 or 85 or 86, correspondingto the hundred and to the ten transmit a signal to the corresponding decade connection. When the short-circuit corresponding to the required position occurs, the corresponding AND-gate 87 or 88 or 89, and the OR-gate 90, transmit the square-wave positioning signal.

The invention of course, is not limited to the embodiments described. For instance, it is possible to replace the guide slides moved by lead screws along the co-ordinate axes by mechanical systems providing a similar function, such as a cable or wire with a return pulley, or a tubular linear motor. These systems help inter alia to reduce mechanical inertia and hence the power consumption for positioning control. Also, lead screws may flex and thus slightly reduce positioning control accuracy.

Also, although the embodiments described in detail relate to wiring machines, the invention of course embraces any form of position control at a number of discrete places, linearly or with respect to a working surface, the distribution of such places not necessarily being uniform.

The short-circuiting device can be of any kind. It may in some cases be convenient if the strips are separated by a photoconductive substance, short-circuiting being produced by impingement of a narrow light beam.

What we claim as our invention and desire to secure by Letters Patent is:

l. A machine for performing operations consecutively at preselected working positions, comprising: a carrier member; at least one moving means for said carrier member; a drive system to move said moving means in either direction along a co-ordinate axis; a scale extending along said coordinate axis,

said scale comprising a plurality of transverse conductive strips insulated from adjacent strips; said moving means including a short-circuiting member adapted to short-circuit any two adjacent strips of its scale in the direction of movement of said moving means; an electronic logic circuit; detector means in said logic circuit to detect a short-circuit between the two adjacent strips in registration with a preselected working position; and means in said logic circuit initiating stopping of said drive system at the commencement of said short-circuit and restarting said drive system in the opposite sense after a predetermined time interval, to provide accurate iterative positioning of said moving system in registration with said preselected working position.

2. A machine according to claim 1 in which said logic circuit produces a square-wave signal of predetermined duration at connections to two adjacent strips of said scale, in response to short-circuiting of said adjacent strips; and said logic circuit effects stopping of said drive system in response to the rising leading edge of said square-wave signal, and operation of said drive system in the opposite sense in response to the falling trailing edge of said square-wave signal.

3. A machine according to claim 2 in which said scale includes an insulating support and said conductive strips of said scale project from said support; and said short-circuiting member comprises a roller at least the rolling surface of which is conductive and which is operatively connected to said moving means to be moved over said scale in the direction of said co-ordinate axis.

4. A machine according to claim 5 in which the radius of said roller is so related to the width of the gap between said two adjacent strips that, even after wear of the contact edges of said adjacent strips, said roller contacts only said strips and not said insulating support.

5. A machine according to claim 3 in which said roller is mounted on a spindle with a clearance so related to the width of the gap between said two adjacent strips and to the speed of movement of said roller that said roller makes a short-circuit of predetermined duration between said strips.

6. A machine according to claim 1 in which each said two adjacent strips represent a position data bit; and which includes a sub-circuit interconnecting said strips and said logic circuit to encode said position data.

7. A machine according to claim 6 in which some of said conductive strips of said scale are arranged in the form of two interdigitated combs, each of said strips which forms one tooth of either of said combs being disposed between two strips not belonging to the same comb.

8. A machine according to claim 6 in which said interconnections correspond to decimal-coded binary encoding.

9. A machine according to claim 8 in which said conductive strips are numbered from 0; the even-number strips are in the form of two half-strips insulated from one another; the oddnumber strips are interconnected in groups of five consecutive strips to decade output connections; and said 0-strip and said half-strips are connected to ten unit output connections, the first strip or half-strip being connected to the first of said unit output connections, the second strip or half-strip being connected to the second of said unit output connections, and so 10. A machine according to claim 1 in which said scale, at both ends of said plurality of strips which constitute a working zone, has further strips; and in which there are connections from said further strips to said logic circuit to control at least the braking of said drive system to prevent said moving means moving out of said working zone.

11. A machine according to claim 1 in which said scale has a plurality of rows of strips connected in the same order to said logic circuit, each said row providing positioning to a different pitch.

12. A machine according to claim 1 in which said logic circuit includes comparator means for comparing the co-ordinate of any working position with the co-ordinate of the immediately previously working position, and means for controlling the movement of said drive system in the sense appropriate to such comparison.

13. An electronic circuit wiring machine for performing wiring operations consecutively at predetermined working positions identified by co-ordinates from two perpendicular co-ordinate axes; comprising a wiring tool carrier member; two slide means for said carrier member movable respectively parallel to said co-ordinate axes; two drive systems, respectively to move each said slide means in either direction parallel to the respective co-ordinate axis; a scale extending along each of said co-ordinate axes, each of said scales compring a plurality of transverse conductive strips each insulated from adjacent strips; each said slide means including a short-circuiting member adapted to short-circuit any two adjacent strips of its associated scale in the direction of movement of said slide means; an electronic logic circuit; detector means in said logic circuit to detect short-circuits between the two adjacent strips in registration with a preselected working position; and means in said logic circuit initiating stopping of said drive systems at the commencement of said short-circuit and restarting said drive systems in the opposite sense after a predetermined time interval, to provide accurate iterative positioning of said slide means in registration with said preselected working position.

14. An electronic circuit wiring machine according to claim 13, in which at least one of said two scales has two rows of strips, providing two different pitches. 

1. A machine for performing operations consecutively at preselected working positions, comprising: a carrier member; at least one moving means for said carrier member; a drive system to move said moving means in either direction along a co-ordinate axis; a scale extending along said co-ordinate axis, said scale comprising a plurality of transverse conductive strips insulated from adjacent strips; said moving means including a shortcircuiting member adapted to short-circuit any two adjacent strips of its scale in the direction of movement of said moving means; an electronic logic circuit; detector means in said logic circuit to detect a short-circuit between the two adjacent strips in registration with a preselected working position; and means in said logic circuit initiating stopping of said drive system at the commencement of said short-circuit and restarting said drive system in the opposite sense after a predetermined time interval, to provide accurate iterative positioning of said moving system in registration with said preselected working position.
 2. A machine according to claim 1 in which said logic circuit produces a square-wave signal of predetermined duration at connections to two adjacent strips of said scale, in response to short-circuiting of said adjacent strips; and said logic circuit effects stopping of said drive system in response to the rising leading edge of said square-wave signal, and operation of said drive system in the opposite sense in response to the falling trailing edge of said square-wave signal.
 3. A machine according to claim 2 in which said scale includes an insulating support and said conductive strips of said scale project from said support; and said short-circuiting member comprises a roller at Least the rolling surface of which is conductive and which is operatively connected to said moving means to be moved over said scale in the direction of said co-ordinate axis.
 4. A machine according to claim 5 in which the radius of said roller is so related to the width of the gap between said two adjacent strips that, even after wear of the contact edges of said adjacent strips, said roller contacts only said strips and not said insulating support.
 5. A machine according to claim 3 in which said roller is mounted on a spindle with a clearance so related to the width of the gap between said two adjacent strips and to the speed of movement of said roller that said roller makes a short-circuit of predetermined duration between said strips.
 6. A machine according to claim 1 in which each said two adjacent strips represent a position data bit; and which includes a sub-circuit interconnecting said strips and said logic circuit to encode said position data.
 7. A machine according to claim 6 in which some of said conductive strips of said scale are arranged in the form of two interdigitated combs, each of said strips which forms one tooth of either of said combs being disposed between two strips not belonging to the same comb.
 8. A machine according to claim 6 in which said interconnections correspond to decimal-coded binary encoding.
 9. A machine according to claim 8 in which said conductive strips are numbered from 0; the even-number strips are in the form of two half-strips insulated from one another; the odd-number strips are interconnected in groups of five consecutive strips to decade output connections; and said 0-strip and said half-strips are connected to ten unit output connections, the first strip or half-strip being connected to the first of said unit output connections, the second strip or half-strip being connected to the second of said unit output connections, and so on.
 10. A machine according to claim 1 in which said scale, at both ends of said plurality of strips which constitute a working zone, has further strips; and in which there are connections from said further strips to said logic circuit to control at least the braking of said drive system to prevent said moving means moving out of said working zone.
 11. A machine according to claim 1 in which said scale has a plurality of rows of strips connected in the same order to said logic circuit, each said row providing positioning to a different pitch.
 12. A machine according to claim 1 in which said logic circuit includes comparator means for comparing the co-ordinate of any working position with the co-ordinate of the immediately previously working position, and means for controlling the movement of said drive system in the sense appropriate to such comparison.
 13. An electronic circuit wiring machine for performing wiring operations consecutively at predetermined working positions identified by co-ordinates from two perpendicular co-ordinate axes; comprising a wiring tool carrier member; two slide means for said carrier member movable respectively parallel to said co-ordinate axes; two drive systems, respectively to move each said slide means in either direction parallel to the respective co-ordinate axis; a scale extending along each of said co-ordinate axes, each of said scales compring a plurality of transverse conductive strips each insulated from adjacent strips; each said slide means including a short-circuiting member adapted to short-circuit any two adjacent strips of its associated scale in the direction of movement of said slide means; an electronic logic circuit; detector means in said logic circuit to detect short-circuits between the two adjacent strips in registration with a preselected working position; and means in said logic circuit initiating stopping of said drive systems at the commencement of said short-circuit and restarting said drive systems in the opposite sense after a predetermined time interval, to provide accurate iterative positioning of sAid slide means in registration with said preselected working position.
 14. An electronic circuit wiring machine according to claim 13, in which at least one of said two scales has two rows of strips, providing two different pitches. 